Broadcast (including multicast) transmissions of data (e.g., over Multimedia Broadcast Multicast Service “MBMS” bearers or over Digital Video Broadcast for handhelds “DVB-H”) is an efficient technique for simultaneously delivering content data to a plurality of clients. However, as typical broadcast schemes are unidirectional, content data cannot be broadcasted in a reliable manner that ensures the integrity of the broadcasted content data. This unreliability is due, in part, to the fact that a receiving side (e.g., a client) cannot send information associated with received or missing data packets (or other information pertaining to the broadcast) during an ongoing broadcast session.
For small scale broadcasts of data, traditional error control techniques (e.g., point-to-point data repair) may be utilized, however, for large scale broadcasts, it is not feasible to scale up such techniques for use by a multitude of users. For example, performance degradation or even system failure may result from implosions that occur when a loss of a packet triggers simultaneous messages from a plurality of users or exposure that occurs when a plurality of recovery-related messages (e.g., retransmission of packets) are received by users that have not experienced any packet loss.
There are two types of conventional broadcast protocols that have been widely adopted, namely automatic repeat request (“ARQ”) based protocols and forward error correction (“FEC”) based protocols. With ARQ protocols, a sender retransmits data upon requests from a user. With FEC protocols, the data that is broadcasted is encoded to obtain some parity data that can be used to verify and, if needed, correct the broadcasted content data. In addition, hybrids of the ARQ and FEC protocols have also been proposed. While these techniques provide enhanced data delivery in some circumstances, the typical broadcast protocol uses a single multicast channel or group. In other words, all packet transmissions and retransmissions are conducted over a single broadcast channel. Each user therefore receives all of the retransmissions of a packet, even if it has previously received the correct form of the packet.
Another type of broadcast protocol that has been adopted is the Reliable Multicast Transport Protocol (“RMTP”). RMTP provides sequenced, lossless delivery of a stream of packets from a broadcaster to a group of users and is based on a multi-level hierarchical approach, in which the users are grouped into a hierarchy of local domains, with a Designated Receiver (DR) in each local domain. Users in each local domain periodically send acknowledgments (ACKs) to their corresponding DR, DRs send ACKs to higher level DRs, until the DRs in the highest level send ACKs to the broadcaster, thereby avoiding the ACK-implosion problem. DRs may also provide repair data to the users in response to request for retransmission of packets.
One significant drawback of conventional broadcasting and multicasting protocols is that they all operate in bi-directional systems. Therefore, such protocols cannot be used in connection with arrangements where the user receiving the broadcasted content data may not have an uplink to the broadcaster until after the broadcast has been completed. This limitation prevents such conventional broadcasting techniques from being implemented in applications such as mobile communications terminals (e.g., mobile phones) where system-wide constraints require that simultaneous bi-directional data transfer be minimized whenever possible.
Accordingly, it will be appreciated that there remains a need for a reliable technique for the bulk delivery of data over broadcast bearers that is scalable and allows for point-to-point data repair and other post-processing transactions.